Signal relaying circuit



Feb. 12, 1935. w KNQOP I 1,990,552

' SIGNAL RELAYING CIRCUIT Filed A ril 50, 1951 lNVEN TOR I W A. KNO 0P ATTORNEY UN lTE I STATES PATENT FFlCE SIGNAL RELAYING CIRCUIT William A. Knoop,

HempsteadyN. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application April 30, 1931, Serial No. 534,108

4 Claims. (Cl. 178-70) This invention relates to relay circuits and more particularly to circuits for operating sensitive polarized relays by relatively weak electrical impulses such as are transmitted over ocean cables.

An object of the invention is to associate a sensitive instrument with an impulse receiving circuit through an amplifier in-such manner that the instrument may be operated directly by impulses of uni-directional current in the output circuit of the amplifier, but may be unaffected by the normal uni-directional current traversing the amplifier output circuit.

This invention is an improvement over such arrangements as disclosed in British Patent 165,888 and United States Patents 1,609,805, 1,649,341 and 1,717,624, respectively granted to W. N. Fanning on December '7, 1926, November 15, 1927, and R. H. Ranger on June 18, 1929.

In some instances it is desirable to operate a very sensitive relay by means of weak impulses which are amplified before being impressed upon the relay. It may also be desirable in order to employ relays of high sensitivity to maintain the path in which the relay winding is connected free from normal uni-directional current which traverses the amplifier output circuit. This may, of course, be accomplished by the use of a transformer, but a transformer ordinarily necessitates the use of an alternating current relay and may also introduce other disadvantages which are inherent in transfer of very low frequency impulses by transformers. To obviate these disadvantages, it has been suggested that the sensitive direct current instrument be connected in a bridge path between impedance arms, one of which forms a portion of the amplifier output circuit and another of which is an element having an impedance equal to the normal impedance of the external output circuit arm. Such an arrangement is, however, not conducive to distortionless transfer of impulses for the reason that the fixed arm impedance is balanced against an impedance which is non-linear. .In other words, the increase of current through the variable impedance arm when a' positive potential is impressed upon the input circuit of the amplifier diifers in magnitude from the decrease in that same current when an equal negative potential is impressed upon the input circuit of the amplifier. Balanced or push-pull amplifiers may, of course, be employed to prevent such distortion in the input circuit, but all balanced amplifiers do not w themselves to direct association with a'circuit one side of which is grounded.

In accordance with the present invention, a sensitive polarized relay is associated with a circuit over which relatively weak electrical im- 5 pulsesare transmitted and one side of which may be grounded, by means of an amplifier the input terminals of which are connected directly to the circuit. The relay is connected in a balanced bridge or normal zero current path. 10 When the arms of the bridge are constituted by impedance elements in the unidirectional output current path of the amplifier, the other two arms of the bridge comprise impedance elements similar to those mentioned and which are con- 15 nected in the. uni-directional output currentpath of an amplifier similar to the first amplifier. In one form of circuit constructed in accordance with the invention the input terminals of this second amplifier are connected to points 20 in the output circuit of the first amplifier in such manner that when the current of the first amplifier tends to increase, that in the second amplifier will tend to decrease. In an alternalend tive form of the. invention the input terminals 25 of the second amplifier are connected to points in the output circuit of a third amplifier whose input terminals are .in effect in parallel to that of the first amplifier.

A feature of the invention is'the obtaining of a decrease in distortion in the output of the amplifier tubes with an increase of range over which the tubes are satisfactorily operated. j

Another feature is the more efiicient, use of a plate battery voltage than heretofore employed 35 in operating sensitive relays with amplified impulses corresponding to those received over long transmission lines.

Still another feature is the provision of arrangements wherein the windings of .the relays are connected across the plate circuits of the amplifiers instead of in series with such circuits, as disclosed in the abovementioned patents. The applicants arrangements avoid the adjustments sometimes required to overcome different magnetic effects produced in relay cores having different permeability values.

Other objects and. features will be found in the following detailed description of certain em- 6 bodiments of the invention and in the appended claims when taken in conjunction with the accompanying drawing of which:

Fig. 1 illustrates a preferred embodiment of the invention; and.

Fig. 2 shows a modification of Fig. 1;

Like parts are designated by like reference characters.

' Referring to Fig. 1, an incoming line 11 is connected directly to amplifier tube 12. Gridbattery 13 is of such value as to operate tube 12 at the mid-point of its grid potential-plate current characteristic whereby incoming positive and negative .impulses are repeated with a minimum distortion. The plate circuit of tube 12 extends over resistances 14 and 15 in series, contacts 16 and 17 of a differential indicating device 18, battery 19, to the filament of tube 12.

Resistance 14 serves as a potentiometer whereby a portion of the output voltage of tube 12 is impressed through a condenser 20 onto the,

grid of a second stage amplifier tube 21. Condenser 20 is made of sufllciently large capacity, say about 4 microfarads, so that it does not appreciably afiect the shape and phase of the signal components. Amplifier tube 21 has a grid potential-plate current characteristic similar to that of tube 12 and its grid is biased by a battery 22 so as to operate this tube also at the midpoint of its characteristic. The plate circuit of tube 21 extends over resistances 23 and 24 in series, terminals 25 and 17 of the differential indicating device 18, battery 19, to the filament of tube 21. The values of the resistance elements have preferred values of say, 300 to 3000 ohms for each of resistances 14 and 23 and 500 ohms for each of resistances 15 and 24.

Bridged across the plate circuits of tubes 12 and 21 at points 26 and 27 is a path including a sensitive polar relay 28 referred to in places herein as a direct current instrument. The plate circuits are therefore arranged to form a Wheatstone bridge arrangement comprising four arms each constituted of one of the resistance ele-" ments, and a normally balanced bridge contain- 'ing the relay 28. By making resistance 23 adjustable, the arrangement is capable of being balanced for the normal space currents of the two tubes whereby the relay normally remains inert. The input terminals of tube 21 are connected to terminals in the output circuit of tube 12 in the manner shown so that when the space current of tube 12 tends to increase in response to an incoming signal impulse, that of tube 21 will tend to decrease and vice versa.

Thus when relatively weak incoming signals are received over line 11 they are amplified in opposite phase by tubes 13 and 21 and the resulting difference in potential between points 26 and 2'7 is effective to cause the operation of relay 28 in the direction corresponding to the polarity of the incoming signal impulses. The differential device 18 gives an indication of the nature of the impulses received.

In the modification of the invention shown in Fig. 2, the arrangement shown is similar to that of Fig. 1 except that connected to the line 11 in parallel with tube 12 is another tube 29 arranged to give amplification of unity and provided for the purpose of shifting the phase of the line voltage 180 whereby the proper phase difference between the voltages respectively applied to the grids of amplifier tubes 12 and 21 may be obtained. Thus, regardless of whether or not the line is grounded, the entire line voltage can be applied to the grid of one of the amplifier tubes,

a voltage of equal value and opposite phase being applied to the grid of the other amplifier tube, and the filaments of all the tubes can be grounded. The adiustment of potentiometer 30 is such that the voltage appliedto the input.

circuit of tube 21 is equal, though opposite in phase, to the voltage applied to the input circuit of tube 12. 1

. It naturally follows thentthat by providing output circuits for the two \amplifier tubes in push-pull relation as shown in Figs. 1 and 2, which tubes are normally balanced, the output resulting from the incoming signal will have practically no distortion and this will permit an increase in the range over which each tube may be satisfactorily worked.

In these arrangements a more efficient use of the plate battery voltage is obtained with the same elements used in arrangements heretofore employed, as disclosed in United States Patent 1,639,929, granted to A. M. Curtis on August 23, r

1927. In the arrangement of the present invention, it will be assumed that the resistances 14 and 23 are each of 1000 ohms, resistances 15 and 2'4 are-each of 300 ohms, the plate voltages of the tubes 12 and 21 are each 130 volts and the current flow indicated on milliammeter 18 is 40 milliamperes, then the battery voltage required will be EB=EP+IR =130-i-20X10- (1000-H300) =130+26=156 volts Ep is the plate voltage.

It is to be noted that the 40 milliamperes indicated on the milliammeter 18 is a record of the current in the plate circuits of both tubes, and, therefore, half flows through each circuit.

Assuming that the tubes 12 and 21 are similar in character and are to be operated at the same point of their grid potential-plate current characteristics, it is evident that the plate voltages of the tubes are of the one value.

It is to be also noted that no diluting resistance is required-in the present invention, and therefore the energy that would be otherwise dissipated by such resistance, is saved.

What is claimed is:

1. In combination, a transmission circuit upon which impulses of opposite polarity may be impressed, an electron discharge relay having its input terminals conductively connected to said circuit, a polarized relay connected to the output terminals of said electron discharge relay, and means comprising a second electron discharge relay connected intandem with the first mentioned discharge relay and a normally balanced bridge circuit for connecting said polarized relay between theoutput terminals of said electron discharge relays for preventing flow of current through said polarized relay except when impulses are impressed upon said receiving circuit.

2. In combination, a transmission circuit, two electron discharge relays having their input circuits connected in series to said transmission circuit in such manner that an impulse impressed on the input circuit of one relay causes the space current of that relay to decrease, which decrease causes the space current of the other relay to increase, and a direct current instrument having its terminals connected .to

points in the space current paths of said electron discharge relays, which points are normally at the same potential when no signal impulse is impulse impressed on the input circuit of one relay causes the space current of that relay to decrease, which decrease causes the space current of the'other relay to increase, plate circuits for said relays connected in parallel to form a balanced Wheatstone bridge arrangement, a source of voltage common to said plate circuits, and a direct current instrument having its terminals connected to points in said plate circuits which points are of the same potential when no impulse is being received by said transmission circuit but at difierent potentials when signal impulses are being received.

4. In combination, a signal receiving circuit, two electron discharge relays having their input terminals connected thereto in parallel relation, a third electron discharge relay having its input terminal connected with the output terminal of one of said first named relays in such manner as to have its space current vary in opposite manner to that of the other two relays, a polarized relay having one terminal connected to a point in the space current path of said (third electron discharge relay and its other terminal connected to a point in the space current path of one of the other of said relays, said points being normally at the same potential when no impulses are being received by said receiving circuit.

WILLIAM A. HOOP. 

